Nobody is paying premium value for Letang or Malkin with their trade protection, age and cap hits.
And if they are Pittsburgh is taking back cap dumps which doesn’t align itself with why Rutherford would be moving Malkin or Letang.
You should consider it from Pittsburgh's perspective, vs from other teams.
If Malkin plays well - he's still in contention for the best player in the world. Literally. He was so good early this season when Crosby got injured. If you get offended by "best" in the world, let's instead say top 3 or so.
He also has a fantastic playoff track record, despite recent misses, so it's not like he can't step up in playoffs.
Pittsburgh will never get close to that value. Trading Malkin would essentially be throwing in the towel on a cup run and going for rebuild. Which would be crazy, with Crosby still at the end of his prime.
Your only option really is to ride it out with Crosby/Malkin a few more years. Tweak/re-tool around them, and hope both can perform next season and especially come playoffs. If both Malkin and Crosby perform near top of their ability in the playoffs - Pittsburgh arguably remain the team to beat, or close.